Cathode-ray tube with laminated safety panel and separate light-attenuating layer

ABSTRACT

A cathode-ray tube comprising an evacuated envelope including a viewing window, and a transparent glass safety panel laminated to the window with an adhesive material. The tube includes a separate nonreflective light-attenuating layer between the adhesive material and at least one of the window and the panel.

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l 73 xii 3,708,622

United States Patent 1 91 1111 3,708,622

Brown, Jr. et al. 1 51 .Jan. 2, 1973 54] CATHODE-RAY TUBE WITH -[56] References Cited LAMINATED SAFETY PANEL AND A I SEPARATE LIGHT-ATTENUATING UNTED STATES PATENTS LAYER 3,362,804 1/1968 Hamilton ..17s 7.s2 3,610,994 10/1971 Sheldon ....178/7.82 1 Inventors: Malcolm George Brown, J 3,614,519 10/1971 Figlewicz ..l78/7.-82

caster; Gilbert James Guille, Jr., l George Ernest o g, Primary ExaminerHoward W. Britton Lititz, all of Pa. Attorney-Glenn H. Bruestle 73 Assignee: RCA Corporation [57] I ABSTRACT [22] Filed: Sept' 1971 A cathode-ray tube comprising an evacuated envelope [21] App1.N0.: 184,094 including a viewing window, and a transparent glass safety panel laminated to the window with an adhesive material. The tube includes a separate nonreflective [52] U.S. Cl. ..l78/7.82, 350/276 SL ght-attenuatmg layer between the adheswe matenal [51] Int. Cl. ..G02b 5/22, 1-101 29/06, H01 29/22 and at least one of the window and the paneL [58] Field of Search ..178/7.82; 350/276 SL '10 Claims, 4 Drawing Figures Jilin #:35-

PATENTEDJAN 2 I975 INVENTORS. Malwlm 6.5mm Jr. Gilbert J Gull/e, Jr. and

6e0rge Lang/31H. BY

ATTORNEY CATHODE-RAY TUBE WITH LAMINATED SAFETY PANEL AND SEPARATE LIGHT- ATTENUATING LAYER BACKGROUND OF THE INVENTION This invention relates to a cathode ray tube having a glass safety panel laminated to the viewing window of the tube.

Some types of cathode-ray tubes, particularly television picture tubes, have a glass safety panel laminated to the viewing window of the tube in order to reduce the danger of implosion and also, should the tube implode, to reduce the danger of injury to people and things nearby. Some prior structures and methods of preparation are described in U.S. Pat. Nos. 3,079,363 to S. D. Koch et al., 3,061,580 to W. 0. Erickson et al., 3,321,099 to R. L. Carlyle et al. and 3,334,008 to R. E. Park et al.

In order to improve the contrast of the video image with its background when the tube is operated in ambient light, it is a common expedient to tint the viewing window and/or the glass safety panel to have a neutral density transmission which is less than that of clear glass. The light of the video image from the viewing screen behind the window is attenuated as it passes through the safety panel to the viewer. Ambient light reflected from the viewing screen must make two passages through the panel and window. Thereby, the contrast of the video image is improved. The amount of contrast and brightness of the video image increases with the amount of tinting in the safety panel and the window; The tinted safety panels are supplied to the tube maker. It is common practice for the tube maker to carry a-large inventory of glass panels of three different values of light transmission in each tube size.

SUMMARY OF THE INVENTION light-attenuating layer is preferably comprised of lightopaque particles and a binder in such proportions that the laminated structure has a light transmission of about 50 to 80 percent of a similar structure with a fully transmitting glass panel.

Some of the advantages of the novel structure over similar previous tinted laminated structures are as follows. The light-attenuating layer may be produced by the tube maker as it is needed. Hence, the tube maker need only carry an inventory. of safety panels of different sizes but only one light-transmission value in each panel size. Also, the tube maker can produce panels with the desired light-attenuating layers as they are needed, thereby shortening the lead time and commitment for such panels. The novel structure may be made in any of a wide range of light transmissions according to the customers order instead of being limited to the particular light transmissions that are available from the supplier. The higher transmission glass is more economical since it is produced in larger quantities for numerous applications whereas lower transmission glass is produced in smaller quantities for comparatively few applications.

BRIEF DESCRIPTION OF THE DRAWING viewing window of still another cathode-ray tube showing light-attenuating layers on both the inner panel surface and the outer window surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical cathode-ray tube of the invention is shown in FIGS. 1 and 2. It is comprised ofa vacuum-tight envelope 21 including a neck portion 23, a funnel portion 25 and a viewing window 27. A glass safety panel 29 is attached to the outer surface of the viewing window 27 with an adhesive layer 31. A band of plastic tape 33 encircles the joint between the window 27 and the safety panel 29. A luminescent screen or target 35 is located adjacent the inner surface of the viewing window 27. An electron gun 37 is located insidethe neck portion 23 of the tube and is adapted during the operation of the tube to project one or more beams of electrons toward the screen 35 to excite selected portions of the screen to luminescence.

One embodiment of the invention is illustrated in FIG. 2 wherein an enlarged section through the viewing window 27 shows the safety panel 29, the adhesive layer 31, and the luminescent screen 35. A separate, nonreflective, light-attenuating layer 39 comprised of light-opaque particles in a binder is located between the inner surfaceof the safety panel 29 and the adhesive layer 31. This embodiment of the invention is conveniently made by coating theglass safety panel, which .is relatively light in weight and small in bulk, as

described below, prior to its assembly into the tube. I

Another embodiment of the invention is illustrated in FIG. 3 wherein an enlarged section through the viewing window 27a shows the glass safety panel 29a, the adhesive layer 31a and the luminescent screen 35a. A separate, non-reflective light-attenuating layer 41comprised of light-opaque particles in a binder is located between the outer surface of the viewing window 27a and the adhesive layer 31a. This embodiment is less conveniently made than the embodiment disclosed in FIG. 2 because the window must be coated either before evacuation of the tube (thereby requiring special handling during the subsequent tube fabrication) or after evacuation of the tube (thereby requiring coating on the surface of the essentially completed tube, which is heavy and bulky). Nevertheless, this embodiment can bemade in a practical manner if it is otherwise desirable.

Still another embodiment of the invention is illustrated in FIG. 4 wherein an enlarged section through the viewing window 2711 shows the glass safety panel 29b, the adhesive layer 31b, and the luminescent screen 35b. There are two nonreflective, light-attenuating layers 43 and 45, each comprised of light-opaque particles in a binder. The first layer 37 is located between the outer surface of the viewing window 27b and the adhesive layer 31b. The second layer 39 is located between the adhesive layer 31b and the inner surface of the safety panel 29b.

In each of the embodiments, light from the video image is generated in the luminescent screen 35, 350 or 35b and passes only once through the light-attenuating layers 39, 41, or 43 and 45 in its transit to a viewer; whereas ambient light, which emanates from sources outside the tube, must pass through the light-attenuating layers 39, 41, or 43 and 45 twice in its transit to a viewer.

The viewing windows 27, 27a and 27b and the glass safety panels 29, 29a and 29b may have a light transmission which is close to 100 percent of that of air or may be tinted to have some lower light transmission. The nonreflective light-attenuating layers 39, 41, 43 and 45 may have a light transmission of about 50 to 80% of that of air. This corresponds to a light attenuation of about 50 to 20 percent respectively. The attenuation is achieved by the combination of layer thickness and concentration of light-opaque particles in the layer. The light-attenuating layers are usually about 0.01 to 1.0 mil thick. The lighteopaque particles usually constitute about 20 to 60 volume percent of the light-attenuating layer.

Any of a number of materials may be selected as the binder for the light-attenuating layer. The binder preferably has the following properties. It should be transparent or translucent. It should have an adhesion to glass equal to or better then the adhesive material used to laminate the safety panel to the viewing window. It should have a viscosity (either as is or through dilution with solvent) such that it can be coated on a glass surface in thin uniform layers by the method of application chosen. Examples of materials which meet these requirements for spraying, dipping, flowing or spinning are methyl silanes, high-molecular-weight rapid-film-forming polyvinyl acetates, methacrylated chromic halides, and polyvinyl butyrals. Best results have been obtained using polyvinyl butyral XYLS marketed by Union Carbide Company, New York, New York. Inorganic compounds such as silicates can be used especially because chemically they resemble a glass surface, thus providing the required. surface for bonding by the adhesive material.

A nonreflective, neutral density filter is obtained by incorporating finely divided light-opaque particles into the binder material. The phrase light-opaque particles includes particles which absorb and/or block light. The light-opaque particles are preferably black colored to the naked eye. Various commercial materials can be used to provide light-opaque particles; for example, India ink such as marketed by Higgins Ink, Newark, N. J., Celutate Black marketed by Harshaw Chemical Company, Cleveland, Ohio, or Carbolac-l marketed by Cabot Company, Boston, Mass. Best results were achieved with Alcoblak 322 marketed by Columbian Division, Cities Service Company, New York, New York. The foregoing commercial materials include finely divided carbon particles. Alternatively, the light-opaque particles may be of one or more inorganic materials such as particles of manganese dioxide, or nickel oxide. The light-absorbing particles may be particles of one or more organic dyes or lakes provided the dye or lake does not degrade or adversely affect the adhesion or other necessary properties of the adhesive layer.

The nonreflective, lightattenuating layer may be applied by any known coating process for the coating material selected. Spray-coating, dip-coating, flowcoating, and spin-coating are examples of suitable coating processes. Best results have been obtained by spraying the spray formulation after dilution with an appropriate solvent. Dilution with solvent lowers the viscosity to the value required for the spray equipment that is to be used. Viscosity can also be adjusted to suit a dipping operation. During the coating step, care should be taken to allow for solvent evaporation, otherwise nonuniformities may occur in the finished coating. Conventional techniques for spray painting provide excellent guide lines to follow in applying the coating by spraying.

The light transmission of the coating can be monitored during the coating steps in order to determine when the exact required transmission has been reached. This can be accomplished by using a light source and a photocell equipped with shutters to prevent the coating from accumulating on the optics of the monitoring system. Once process controls have been established, the monitoring equipment need be used only for final inspection.

The designer of the viewing window structure may, for reasons of structural strength and/or weight, cause the thickness of the viewing window to vary from center to edge. This variation in glass thickness causes the glass transmission to vary according to the equation transmission e' where p. absorption coefficient a constant for a particular glass and t= thickness of the glass.

This variation in transmission and hence contrast can be avoided with the invention by using a higher transmission viewing window glass, thus minimizing the absolute variation in transmission. The light-attenuating layer can be produced in relatively uniform thickness, and hence uniform transmission can be held within close tolerances. Or, the thickness of the light-attenuating layer, because of the characteristics of the coating method used, can be provided in such thickness as to compensate for variations in thickness of the viewing window so that the overall transmission of the viewing window and the light-attenuating layer is relatively uniform.

EXAMPLE 1 A spray formulation is prepared using the following recipe. Mix 881 grams of isopropanol (technical grade or equivalent) with 63 grams of isobutanol (technical grade or equivalent). Into this mixture, blend 51 grams of XYLS polyvinyl butyral resin solution (20 percent solids in isopropanol such as marketed by Union Carbide Corp, New York, New York) and then 5 grams Alcoblak 322 carbon suspension (25 percent carbon in isopropanol as marketed by Columbian Division, Cities Service Company). The total mixture should then be homogenized for about 20 minutes 'to provide the spray formulation. This spray formulation is sprayed onto the interior surface of a clean glass safety panel with an automatic spray machine. The thickness of the material is built up until the desired light transmission is reached, for example, 75 percent transmission. The transmission can be determined with the use of a transmission measuring device, such as a light source and photocell calibrated to detect transmission. The spray coating is dried in air, with or without the aid of heat and/or forced draft. The spray-coated glass panel is then laminated to the viewing window of a cathode-ray tube in any known manner producing a structure of the type shown in FIG. 1.

EXAMPLE 2 Follow the procedure described in Example 1 except increase the total solvent percentage in-the spray formulation to allow the use of a hand spray unit. The same materials are used, but the following amounts are typical for a hand spray formulation:

823 grams isopropanol 145 grams isobutanol 29 grams XYLS polyvinyl butyral resin 3 grams Alco-blak 322 The materials are homogenized for about 20 minutes to provide the spray formulation. The spray formulation is sprayed onto a glass safety panel having about a 100 percent light transmission. The panel should be rotated about 90 after each pass in order to ensure uniformity. The solvent should be given time to evaporate after each pass in order to prevent runs and/or crazing in the coating. in order to reach a light transmission of about 55 percent, about minutes of time should be allocated for spraying the necessary number of passes onto each glass panel. The finished spray coated glass safety panel is then laminated to the viewing window of a cathoderay tube in any known manner producing a structure of the type shown in FlG. 1.

We claim: 1. In a cathode-ray tube comprising (1) an evacuated envelope, said envelope including a viewing window and (2) a transparent glass safety panel laminated to said window with'an adhesive material, the improvement comprising a separate nonreflective, light-attenuating layer between said adhesive material and at least one of said window and said panel.

2. The cathode-ray tube defined in claim .1 wherein said light-attenuating layer is between said adhesive material and said window.

3. The cathode-ray tube defined in claim 1 wherein said light-attenuating layer is between said adhesive material and said panel.

4. The cathode-ray tube defined in claim 1 wherein said light-attenuating layer is a neutral gray filter which attenuates the brightness of transmitted light by at least 20%.

5. A cathode-ray tube comprising 1. an evacuated envelope including a viewing window having a laminating surface on the outside of said envelope,

2. a luminescent viewing screen inside said envelope ad'acent said viewing window,

3 a ransparent glass safety panel having a surface closely spaced from said window and outside said envelope,

4. a separate nonreflective, light-attenuating layer coated on said panel surface, said layer being comprised of light-opaque particles dispersed in I binder, and

5. an organic adhesive material adhering said laminating surface of said window to said coated surface of said safety panel.

6. The cathode-ray tube defined in claim 5 wherei said light-attenuating layer is comprised of carbon particles in an organic binder.

7. The cathode-ray tube defined in claim 5 wherein the binder for said light-attenuating layer is the primer layer normally used to promote the wetting and adherence of the laminating surfaces by said adhesive material.

8. The cathode-ray tube defined in claim 5 wherein said light-attenuating layer is comprised of lightopaque particles dispersed in organic binder.

9. The cathode-ray tube defined in claim 5 wherein said light-attenuating layer is comprised of lightopaque particles dispersed in an inorganic binder.

10. The cathode-ray tube defined in claim 5 wherein said light-attenuating layer is comprised of lightopaque particles of organic material in a binder. 

2. a luminescent viewing screen inside said envelope adjacent said viewing window,
 2. The cathode-ray tube defined in claim 1 wherein said light-attenuating layer is between said adhesive material and said window.
 3. The cathode-ray tube defined in claim 1 wherein said light-attenuating layer is between said adhesive material and said panel.
 3. a transparent glass safety panel having a surface closely spaced from said window and outside said envelope,
 4. a separate nonreflective, light-attenuating layer coated on said panel surface, said layer being comprised of light-opaque particles dispersed in binder, and
 4. The cathode-ray tube defined in claim 1 wherein said light-attenuating layer is a neutral gray filter which attenuates the brightness of transmitted light by at least 20%.
 5. A cathode-ray tube comprising
 5. an organic adhesive material adhering said laminating surface of said window to said coated surface of said safety panel.
 6. The cathode-ray tube defined in claim 5 wherein said light-attenuating layer is comprised of carbon particles in an organic binder.
 7. The cathode-ray tube defined in claim 5 wherein the binder for said light-attenuating layer is the primer layer normally used to promote the wetting and adherence of the laminating surfaces by said adhesive material.
 8. The cathode-ray tube defined in claim 5 wherein said light-attenuating layer is comprised of light-opaque particles dispersed in organic binder.
 9. The cathode-ray tube defined in claim 5 wherein said light-attenuating layer is comprised of light-opaque particles dispersed in an inorganic binder.
 10. The cathode-ray tube defined in claim 5 wherein said light-attenuating layer is comprised of light-opaque particles of organic material in a binder. 